To control a bank of plural elevators, group control is usually conducted to efficiently run these plural elevators. In some elevator systems, a plurality of cars serve in a single shaft. Different greatly from an elevator system where only a single car serves in each shaft, control of such an elevator system is required to not only raise the transportation efficiency but also avoid collision between cars.
For example, the above-mentioned requirement is taken into consideration in Japanese Patent No. 3029168 as known. In that specification, a control scheme is proposed for a horizontally-movable shuttle elevator system where a plurality of independently driven cars are circulated along each common shaft through turnaround spaces provided respectively on the highest and lowest stories. By setting a car approach inhibition zone to each car, the control scheme controls the cars so that each car may not enter this zone of another car.
Another example is described in “Basic studies of shuttle elevator systems for mass transportation in a building”, Atsuya Fujino and two others, Trans. of the Institute of Electrical Engineers (Japan) D, 1997, vol. 117, No. 7, p. 815-822. According to this document, the elevator system evaluates the excursion of each car, etc. When a car is coming closer to a floor at which a hall call has occurred, it is determined based on the evaluation whether to stop the car at the hall in response to the call.
However, since the above-mentioned prior art techniques assume application to horizontally movable shuttle elevator systems, it is difficult to apply them to an elevator system where horizontal movement is not possible. That is, since the cars in a shuttle elevator system are assumed to move in the same direction while they move in the same shaft, withdrawing a car depends on its horizontal movement. Therefore, consideration is not given to how to avoid collision and withdraw a car where horizontal movement is not possible.
Moreover, the above-mentioned prior art techniques have another common drawback in that if a car carrying passengers is stopped for safety, the passengers must wait in the closed space. This psychologically disturbs them although the waiting time is short.
The present invention is intended to solve the above-described problem. It is an object of the present invention to provide an elevator group control apparatus capable of preventing collision and minimizing the frequency of safety stops in an elevator system with plural cars in each shaft while efficiently operating the elevator system.